Strong spin-orbit torque metal superlattice thin film material and preparation method and application thereof

Abstract

The invention discloses a strong spin-orbit torque metal superlattice thin film material, and belongs to the technical field of new spin electron materials. The superlattice thin film material comprises a thin film system formed by heavy metal layers with strong spin-orbit coupling and light metal layers with high-orbit Hall conductivity, wherein the heavy metal layers periodically grow on a substrate; in each period, the thickness of the heavy metal layer with strong spin-orbit coupling is 1-3nm, and the thickness of the light metal layer with high-orbit Hall conductivity is 1-3nm. Electron orbital angular momentum flow accumulation is generated on the surface of the light metal layer, the orbital current is injected into heavy metal with strong spin-orbit coupling, and the orbital current is converted into spin current by utilizing the strong spin-orbit coupling characteristic of the heavy metal layer. Therefore, the spin current generation efficiency of the strong spin orbit torque metal superlattice thin film material can be improved, and the giant damping spin orbit torque efficiency and the low-current-density turnover ferromagnetic layer magnetic moment are realized.

Description

Technical Field

[0001] The invention belongs to the technical field of new spin electronic materials, and in particular relates to a strong spin-orbit torque metal superlattice thin film material and a preparation method and application thereof. Background Art

[0002] With the rapid development of information technology, the miniaturization and low power consumption of traditional electronic devices are facing severe bottlenecks due to the existence of Joule heating of electric current. Electron spin is another property of electrons besides charge, which can be used to transmit and store information, and spintronics was born. Spin electrons have extremely low power consumption in transmitting information, can complete the processing and storage of quantum information, and are ideal media for building quantum information chips. The spin Hall effect (SHE) is the effect of applying a transverse current to generate a vertical longitudinal polarized spin current under the action of spin-orbit coupling. The spin current can be achieved without the movement of charge, realizing a dissipation-free process, so that the sample does not generate Joule heating. On the contrary, the inverse spin Hall effect (ISHE) refers to the process of converting spin current into electric current, which can be used to test the size of the spin current. The strength of the spin Hall effect is reflected in the conversion efficiency of current to spin current, and this conversion efficiency is usually expressed in terms of the spin Hall angle (θ SH ) or with θ SH The damped spin-orbit torque efficiency (ξ DL ). The orbital angular momentum is the fundamental source of spin current. Orbital angular momentum flow (orbital current) can be generated by the orbital Hall effect (OHE) and the orbital Rashba-Edelstein effect (OREE). The concept of the orbital Hall effect is that when the material is subjected to an electric field, an orbital current is generated inside the material in a direction perpendicular to the electric field, thereby generating a net orbital angular momentum accumulation at both ends of the material. The concept of the orbital Rashba-Edelstein effect is to use the symmetry breaking of the material interface. Under the action of the electric field, the electron energy band at the material interface splits, generating orbital angular momentum flows with different polarization directions in the momentum space. The net orbital angular momentum accumulation generated by these two effects can be converted into spin current through spin-orbit coupling after being injected into the adjacent heavy metal layer. The maximum orbital Hall conductivity of light metal (γ-Mn) obtained by first-principles calculations is about 4 times that of Pt spin Hall conductivity, but orbital electronics is an emerging discipline, and orbital current has not yet been fully developed and utilized in the field of spin storage.

[0003] At present, most of the existing research uses Pt as the heavy metal layer to provide spin-orbit coupling, and most of them are double-layer structures, such as Pt / Ti, Pt / CuOx, Pt / TaOx, etc. However, the damping-like spin-orbit torque efficiency of these structures is low, usually below 1, which cannot meet application requirements. Summary of the invention

[0004] The purpose of the present invention is to propose a strong spin-orbit torque metal superlattice thin film material and a preparation method and application thereof in view of the problems existing in the background technology. The strong spin-orbit torque metal superlattice thin film material of the present invention can realize the regulation of the damping-like spin-orbit torque efficiency at room temperature, and has low preparation cost and is suitable for large-scale industrial production.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A strong spin-orbit torque metal superlattice thin film material comprises a thin film system formed by a heavy metal layer with strong spin-orbit coupling and a light metal layer with high orbital Hall conductivity periodically grown on a substrate; in each period, the thickness of the heavy metal layer with strong spin-orbit coupling is 1 to 3 nm, and the thickness of the light metal layer with high orbital Hall conductivity is 1 to 3 nm; the number of periods is n, n≥2; the total thickness of the strong spin-orbit torque metal superlattice thin film material is 4 to 40 nm.

[0007] Furthermore, the heavy metal layer material with strong spin-orbit coupling (SOC) is a metal with 5d or 4f electron orbits, specifically W, Ta, Hf, Gd, etc.; the light metal layer material with high orbital Hall conductivity (lightmetal, LM) is a metal with 3d electron orbits, specifically Ti, Cr, Mn, Cu, etc.; the substrate is a silicon wafer or sapphire substrate with thermal oxidation on the surface.

[0008] Furthermore, the heavy metal layer with strong spin-orbit coupling and the light metal layer with high orbital Hall conductivity are formed on the substrate by physical vapor deposition or magnetron sputtering.

[0009] Furthermore, the strong spin-orbit torque metal superlattice thin film material is obtained by magnetron sputtering a high-purity metal target material, and the specific process is as follows: -4Pa, argon gas is introduced into the vacuum chamber at a flow rate of 24 sccm. After the gas pressure stabilizes to 0.27-0.32 Pa, the magnetron sputtering power supply is turned on, and each target material is pre-sputtered for 10 minutes at a DC power of 30 W. The purpose is to use argon ion bombardment to clean the target surface to remove the surface oxide layer and other impurities. After the pre-sputtering is completed, the target baffle is opened for coating. The coating sequence is to first grow a heavy metal layer with strong spin-orbit coupling at a power of 5 W, and then grow a light metal layer with high orbital Hall conductivity at a power of 10 W. The process of growing heavy metal layers and light metal layers is repeated until the set growth time is reached. The target baffle and the sputtering power supply are turned off to obtain a strong spin-orbit torque metal superlattice thin film material formed by periodic [heavy metal layer / light metal layer]n.

[0010] Specifically, the target material includes a heavy metal target material with a purity of not less than 99.99wt% and a light metal target material with a purity of not less than 99.99wt%.

[0011] A spin-orbit torque reversal magnetic moment storage device comprises a perpendicular magnetic anisotropy magnetic film layer grown on a substrate, and a strong spin-orbit torque metal superlattice film material grown on the magnetic film layer; wherein the strong spin-orbit torque metal superlattice film material is the above-mentioned strong spin-orbit torque metal superlattice film material.

[0012] Furthermore, the perpendicular magnetic anisotropy magnetic film layer is a Pt / Co film or a CoFeB film.

[0013] Furthermore, the thickness of the strong spin-orbit torque metal superlattice thin film material is 4-40 nm.

[0014] The invention provides a strong spin-orbit torque metal superlattice thin film material, which generates electron orbital angular momentum flow (orbital current) accumulation on the surface of the light metal layer, and injects the orbital current into the heavy metal with strong spin-orbit coupling, and utilizes the strong spin-orbit coupling characteristics of the heavy metal layer to convert the orbital current into spin current. This can improve the spin current generation efficiency of the strong spin-orbit torque metal superlattice thin film material, and achieve giant damping spin-orbit torque efficiency and low current density flip ferromagnetic layer magnetic moment.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. The present invention provides a strong spin-orbit torque metal superlattice thin film material, which adopts a periodic structure formed by alternating heavy metal layers and light metal layers, and limits the thickness of the light metal layer to less than 3nm, thereby eliminating the body orbital Hall effect in the light metal. When current is passed through the strong spin-orbit torque metal superlattice thin film material, due to the orbital Raschbach-Edelstein effect at the HM / LM (heavy metal layer / light metal layer) interface, an orbital current will be generated in the superlattice thin film material due to the broken interface symmetry; the orbital current is injected into the strong spin-orbit coupling heavy metal layer and converted into an orbital torque. After the orbital torque in each period accumulates, it diffuses into the perpendicular anisotropic magnetic layer, thereby reversing its magnetic moment. By measuring the critical magnetization reversal current density (J sw ) was tested, and it can be seen that compared with pure Pt, the damping-like spin-orbit torque efficiency of the superlattice film material of the present invention has increased by two orders of magnitude. This shows that it is effective to use orbital current to improve the efficiency of spin current generation in superlattice film materials. When superlattice film materials are applied to flip magnetic moment storage devices, strong spin-orbit torque metal superlattice film materials can effectively reduce the critical flip current density of adjacent perpendicular magnetic anisotropy films, and can be applied to magnetic random access memory to reduce energy consumption and manufacturing costs.

[0017] 2. The present invention provides a strong spin-orbit torque metal superlattice thin film material, preparation method and application, which use lower-cost metals W and Ti instead of Pt, effectively reducing costs; and the method is simple and easy to implement, and can achieve uniform preparation on large-area (8-inch and 12-inch) semiconductor wafers, which is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The room temperature spin torque-ferromagnetic resonance voltage (V) of the strong spin-orbit torque metal superlattice thin film material obtained in Example 1 at a microwave current source frequency of 6 GHz ST-FMR )Test results;

[0019] Figure 2 To change the thickness of the FM layer, the damping-like term spin-orbit torque results are fitted. The value of the damping-like term spin-orbit torque efficiency is the inverse of the intercept;

[0020] Figure 3 These are the magnetization reversal test results of the strong spin-orbit torque metal superlattice film materials (ac) with different W and Ti thicknesses within the period obtained in Example 1 and the comparative example Pt (d). DETAILED DESCRIPTION

[0021] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present invention.

[0022] Example 1

[0023] A strong spin-orbit torque metal superlattice thin film material includes a thin film system [HM / LM]n formed by a heavy metal layer (heavy metal, HM) with strong spin-orbit coupling and a light metal layer (light metal, LM) with high orbital Hall conductivity periodically grown on a substrate; in each period of the multi-period thin film system, the thickness of the heavy metal layer with strong spin-orbit coupling is 1 to 3nm, and the thickness of the light metal layer with high orbital Hall conductivity is 1 to 3nm; the number of periods n = 3. In a single period, the thickness of the heavy metal layer with strong spin-orbit coupling is 1, 2, and 3nm, respectively, and correspondingly, the thickness of the light metal layer with high orbital Hall conductivity is 3, 2, and 1nm, respectively, that is, the thickness of a single period thin film is 4nm.

[0024] A spin-orbit torque reversal magnetic moment storage device comprises a magnetic layer grown on a substrate, and a strong spin-orbit torque metal superlattice thin film material [HM / LM]n grown on the magnetic layer; in a single period of the strong spin-orbit torque metal superlattice thin film material, the thickness of the heavy metal layer with strong spin-orbit coupling is 1, 2, and 3 nm, respectively, and correspondingly, the thickness of the light metal layer with high orbital Hall conductivity is 3, 2, and 1 nm, respectively, that is, the thickness of the single period film is 4 nm.

[0025] A method for preparing a strong spin-orbit torque metal superlattice thin film material specifically comprises the following steps:

[0026] S1: using a heavy metal W target material with a purity of not less than 99.99wt% and a light metal Ti target material with a purity of not less than 99.99wt% as sputtering targets; loading the sputtering targets into the target position of the cavity of the magnetron sputtering equipment;

[0027] S2 uses a thermally oxidized Si substrate as the substrate, which is cleaned with acetone, alcohol, and deionized water, and dried with nitrogen to ensure that the surface of the Si substrate is clean;

[0028] S3 puts the cleaned Si substrate into the magnetron sputtering equipment to grow strong spin-orbit moment metal superlattice [HM / LM] n Thin film materials, the specific process is:

[0029] (1) In 1×10 -4Under a background vacuum of 1.5 Pa, argon gas was introduced into the vacuum chamber at a flow rate of 24 sccm until the pressure stabilized to 0.27-0.32 Pa;

[0030] (2) Under an argon pressure of 0.27 to 0.32 Pa, turn on the magnetron sputtering power supply and pre-sputter each target for 10 minutes at a DC power of 30 W. The purpose is to use argon ion bombardment to clean the target surface to ensure that impurities such as the oxide layer on the target surface are completely removed;

[0031] (3) Open the target baffle, sputter NiFe (30W), W (5W), Ti (10W), and Ta (10W) respectively, and repeat the cycle growth of W and Ti for the required number of cycles. After reaching the set growth time, close the target baffle and the sputtering power supply to obtain the ferromagnetic layer / [W / Ti]3 strong spin-orbit torque metal superlattice thin film material / oxidation protection layer heterojunction structure for testing room temperature spin torque-ferromagnetic resonance;

[0032] (4) Open the target baffle, sputter Pt (10W), Co (10W), W (5W), and Ti (10W) respectively, and repeat the cycle growth of W and Ti for the required number of cycles. After reaching the set growth time, close the target baffle and sputtering power supply to obtain the perpendicular magnetic anisotropy layer / [W / Ti]3 strong spin-orbit torque metal superlattice film material structure for testing magnetization reversal.

[0033] The orbital torque in the strong spin-orbit torque metal superlattice film material is injected into NiFe, and the spin torque-ferromagnetic resonance voltage is generated through the AMR effect. The damped spin-orbit torque efficiency of the superlattice film material is obtained by fitting, such as Figure 1 and 2 The critical magnetization reversal current density of superlattice thin film materials with different HM / LM (W / Ti) thicknesses was tested to verify the improvement of the damped spin-orbit torque efficiency of superlattice thin film materials with different compositions, as shown in Figure 2. Figure 3 shown.

[0034] Through the orbital Raschbach-Eldstein effect at the HM / LM interface and the strong spin-orbit coupling properties of the heavy metal layer, an orbital torque is generated in the superlattice film material and injected into the perpendicular magnetic anisotropy ferromagnetic layer. The room temperature spin torque-ferromagnetic resonance voltage (V) of the strong spin-orbit torque metal superlattice film material with different HM / LM thicknesses was tested. ST-FMR ) can fit the quasi-damped spin-orbit torque efficiency of the material; and the critical magnetization reversal current density test can prove the improvement of the quasi-damped spin-orbit torque efficiency. The test shows that the absolute value of the quasi-damped spin-orbit torque efficiency of the superlattice film material of Example 1 can reach 20 or even higher, which is two orders of magnitude higher than that of pure Pt.

[0035] Comparative Example

[0036] The same steps as in Example 1 are used to first grow an 8nm NiFe film as a magnetic layer, then grow a 12nm Pt layer on the NiFe layer as a spin source layer, and finally grow a 1nm Ta layer on the top layer as an anti-oxidation layer to obtain a NiFe (8nm) / Pt (12nm) / Ta (1nm) heterojunction.

[0037] Next, a room temperature spin torque-ferromagnetic resonance voltage test was performed to test the spin torque-ferromagnetic resonance voltage (V) of the NiFe(8nm) / Pt(12nm) / Ta(1nm) heterojunction obtained in the comparative example and the NiFe(a nm) / [W(x nm) / Ti((4-x)nm)]3 / Ta(1nm) system obtained in Example 1 (where a=4, 5, 6, 7, 8, 9, x=1, 2, 3) obtained in Example 1. mix ), complete the fitting extraction of the damping-like spin-orbit torque efficiency. At room temperature, the absolute value of the damping-like spin-orbit torque efficiency of the [W(xnm) / Ti((4-x)nm)]3 strong spin-orbit torque metal superlattice film material reaches 20 or even higher, while the damping-like spin-orbit torque efficiency of the comparative example Pt is usually around 0.1, which fully demonstrates that by inserting a thin light metal layer into the strong spin-orbit coupling heavy metal, the orbital Raschba-Edelstein effect at the HM / LM interface is used to successfully use the orbital current to significantly improve the damping-like spin-orbit torque efficiency in the superlattice film material.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A strong spin-orbit torque metal superlattice thin film material, characterized in that: The superlattice thin film material is a thin film system formed by a heavy metal layer with strong spin-orbit coupling and a light metal layer with high orbital Hall conductivity periodically grown on a substrate; in each period, the thickness of the heavy metal layer with strong spin-orbit coupling is 1 to 3 nm, and the thickness of the light metal layer with high orbital Hall conductivity is 1 to 3 nm; the number of periods is n, n≥2; the total thickness of the strong spin-orbit torque metal superlattice thin film material is 4 to 40 nm.

2. The strong spin-orbit torque metal superlattice thin film material according to claim 1, characterized in that: The heavy metal layer material with strong spin-orbit coupling is a metal with 5d or 4f electronic orbits, and the light metal layer material with high orbital Hall conductivity is a metal with 3d electronic orbits.

3. The strong spin-orbit torque metal superlattice thin film material according to claim 1, characterized in that: The heavy metal layer material with strong spin-orbit coupling is W, Ta, Hf or Gd, and the light metal layer material with high orbital Hall conductivity is Ti, Cr, Mn or Cu.

4. The strong spin-orbit torque metal superlattice thin film material according to claim 1, characterized in that: The substrate is a silicon wafer or a sapphire substrate with a thermally oxidized surface.

5. The strong spin-orbit torque metal superlattice thin film material according to claim 1, characterized in that: The heavy metal layer with strong spin-orbit coupling and the light metal layer with high orbital Hall conductivity are formed on the substrate by physical vapor deposition or magnetron sputtering.

6. The strong spin-orbit torque metal superlattice thin film material according to claim 1, characterized in that: The strong spin-orbit torque metal superlattice thin film material is prepared by magnetron sputtering, the process is: -4 Pa, argon gas is introduced into the vacuum chamber at a flow rate of 24 sccm, and the magnetron sputtering power supply is turned on after the gas pressure stabilizes to 0.27-0.32 Pa, and the target material is pre-sputtered for 10 minutes at a DC power of 30 W; after the pre-sputtering is completed, the target material baffle is opened for coating, and a heavy metal layer with strong spin-orbit coupling is first grown at a power of 5 W, and then a light metal layer with high orbital Hall conductivity is grown at a power of 10 W. The process of growing heavy metal layers and light metal layers is repeated until the set growth time is reached, and then the target material baffle and the sputtering power supply are turned off to obtain a metal superlattice thin film material with a strong spin-orbit torque.

7. The strong spin-orbit torque metal superlattice thin film material according to claim 6, characterized in that: The target material includes a heavy metal target material with a purity of not less than 99.99wt% and a light metal target material with a purity of not less than 99.99wt%.

8. A spin-orbit torque reversal magnetic moment storage device, characterized in that: It includes a perpendicular magnetic anisotropic magnetic film layer grown on a substrate, and a strong spin-orbit torque metal superlattice thin film material grown on the magnetic film layer; The strong spin-orbit torque metal superlattice thin film material is the strong spin-orbit torque metal superlattice thin film material according to any one of claims 1-7.

9. The spin-orbit torque reversal magnetic moment storage device according to claim 8, characterized in that: The perpendicular magnetic anisotropy magnetic film layer is a Pt / Co film or a CoFeB film.

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